This application is based on and claims the priority under 35 U.S.C. xc2xa7119 of German Patent Application 100 19 187.8, filed on Apr. 17, 2000, the entire disclosure of which is incorporated herein by reference.
This application is related to our copending application entitled AERODYNAMIC NOISE REDUCING STRUCTURE FOR AIRCRAFT WING SLATS, being filed simultaneously on the same date as this application. The entire disclosure thereof is incorporated herein by reference.
The invention relates to a system for controlling the pressure of compressed air supplied to a hollow expandable displacement element, and especially such a displacement element forming a component of an arrangement for reducing aero-acoustic noise generated by the slats on the wings of a commercial transport aircraft.
Various noise sources contribute to the total noise generated during the flight of a modern commercial transport aircraft. Among the various noise sources, aero-acoustically generated noise that results from the flow pattern of air around the aircraft structure is becoming an evermore significant portion of the total flight noise. This is because the noise generated by other sources such as the engines has been reduced in recent years by technical advances of those components. In present day commercial transport aircraft, it is roughly estimated that approximately 50% of the total flight noise during a landing approach is generated by the flow of air around the aircraft At structure, while the other half of the total noise is generated by the engines.
Further improvements, i.e. reductions, in the noise generated by the engines are only practically and economically efficacious if similar technical advances for reducing the aerodynamic flow noise around the aircraft fuselage can be simultaneously achieved. It is becoming especially important to reduce the aerodynamic flow noise in view of ever stricter noise level limits, especially around airports with a high aircraft traffic volume. A major factor contributing to the total aerodynamic flow noise during landing and take-off of a modern commercial transport aircraft, is the noise generated by the airflow around high-lift slats deployed from the leading edges of the wings during the landing and take-off phases.
To facilitate an understanding of the aerodynamic noise generated in connection with the leading edge slats, FIG. 5 of the present 5 application shows representative streamlines of the air A flowing around a generally conventional wing, which is schematically shown in section. The wing arrangement includes a main wing 2, a leading edge slat 1 that is extended or deployed (either pivotally or slidingly) forward of the leading edge of the main wing 2, and a landing flap 11 that is extended or deployed rearward from the trailing edge of the main wing 2. Throughout this specification, the term xe2x80x9cforwardxe2x80x9d and the like refers to the normal forward flight direction of the aircraft, for example the direction in which the aircraft nose and the wing leading edges are oriented. As is generally known, the extended slat 1 and landing flap 11 change the effective camber and angle of attack of the airfoil profile of the wing structure, and also influence the airflow over the surfaces of the wing, so as to increase the lift, e.g. for landing and take-off. In this extended configura tion, the slat 1 is deployed forwardly and downwardly from the leading edge nose 2A of the main wing 2 so as to form a slat air gap 130 between a rearwardly facing concave curved surface 3 of the slat 1 and the convexly profiled leading edge nose 2A of the main wing 2.
On the other hand, during cruise flight, the slat 1 is retracted into a retracted position (not shown) directly on the leading edge nose 2A of the main wing 2 so as to reduce the aerodynamic drag and avoid unnecessary increased lift. In this context, the leading edge slat 1 must be retracted smoothly and flushly against the leading edge nose 2A of the main wing 2, so as to form a substantially continuous aerodynamic contour. Namely, the slat 1 is adjacent to the leading edge nose 2A, with at most only a small, aerodynamically insignificant, gap or space therebetween. Therefore, the rear concavely curved surface 3 of the leading edge slat 1 has a profile curvature substantially matching the convex curvature of the leading edge nose 2A of the main wing 2, so that the slat 1 smoothly matches or mates onto the leading edge nose 2A of the main wing 2 without a resistance-causing gap or discontinuity therebetween.
Unfortunately, the profile curvature of the rear concave surface 3 of the slat 1 may be optimal for mating onto the leading edge is nose 2A of the main wing 2 in the retracted position, but it is not optimal for the airflow through the slat air gap 130 between the leading edge nose 2A and the slat 1 in its deployed position as shown in FIG. 4. As a result, the airflow A forms an eddy or vortex 150 that extends lengthwise along the length of the slat 1 (i.e. in the wing span direction). This vortex 150 involves the turbulent eddy recirculation of air in the hollow space defined and bounded by the rear concave curvature 3 of the slat 1, whereby this space generally has a tapered concave shape or tear-drop shape. This vortex 150 further exhibits or generates a fluctuating fluid pressure field of the affected airflow, which is believed to be the cause of the aerodynamic noise generated in this area. Noise measurements in an aero-acoustic wind tunnel have confirmed that a significant reduction of the noise generated by the extended slat can be achieved by arranging a rigid fairing or filler member in the space along the rear concave curvature 3 of the slat 1, which would otherwise be occupied by the vortex 150.
Attempts have been made in the prior art to reduce the aerodynamically generated noise, especially in connection with the slats and the mounting thereof. For example, a study in this regard was published by Werner Dobrzynski and Burkhard Gehlhar entitled xe2x80x9cAirframe Noise Studies on Wings with Deployed High-Lift Devicesxe2x80x9d, from the Deutsches Zentrum fuer Luft und Raumfahrt e.V. (DLR), Institut fuer Entwurfsaerodynamik, Abteilung Technische Akustic, Forschungszentrum Braunschweig, Germany, at the Fourth American Institute of Aeronautics and Astronautics AIAA/CEAS Aeroacoustics Conference on June 2 to 4, 1998 in Toulouse, France.
Among other things, this study disclosed a proposed noise reducing arrangement in which a sheet metal guide member is pivotally connected to the slat in the area of the concavely curved rear or inner surface of the slat facing toward the leading edge nose of the main wing. This sheet metal air guide can be pivoted relative to the slat. Particularly, the air guide member can be extended or deployed relative to the slat during take-off and landing when the slat is deployed relative to the wing. On the other hand, the sheet metal air guide member will be pivoted against the slat during cruise flight when the slat is to be retracted relative to the wing. While such a proposed solution may have achieved a reduction of aerodynamically generated noise in wind tunnel tests, it is considered that such a solution could never be practically carried out in an actual aircraft construction, for practical reasons.
For example, in the previously proposed arrangement, when the slat is retracted against the leading edge nose of the main wing for cruise flight, the gap between these two components is not sufficiently large for accommodating a rigid air guide member tilted or pivoted inwardly against the rear surface of the slat. On the other hand, if the gap is made larger to accommodate the at air guide member, then a disadvantageous aerodynamic gap or discontinuity would be formed along the aerodynamic contour provided by the slat and the wing in combination. Moreover, if a flexible air guide component is provided, which is to be adapted against the inner contour of the slat in the retracted position, then such a component would not have sufficient strength and stiffness in order to withstand the aerodynamic forces in the deployed condition.
Moreover, such a guide element would be expected to have a tendency to flutter due to the alternating aerodynamic pressure effect, or simply due to a failure to remain sufficiently rigid to withstand the aerodynamic forces. Namely, the proposed sheet metal separating surface or air guide member will be subjected to considerable fluctuating aerodynamic forces, which will presumably excite vibrations or oscillations in the member, since it is only to be pivotally connected to the lower edge of the slat without any further stiffening means. Such fluttering generates a significant noise radiation, which is directly contrary to the object of reducing the noise. Furthermore, a pivotally connected sheet metal member requires additional mechanical movable parts, which leads to an increased total weight of the aircraft, as well as increased manufacturing and maintenance costs. It would also be necessary to construct the pivot joint in such a manner that the transition from the underside of the slat to the joint of the separating surface is free of contour discontinuities or gaps, which makes it necessary to achieve a very high manufacturing accuracy.
Additional problems arise because the contour of the rear surface of the slat as well as the geometry of the slat air gap change over the span width of the wing, so that the air guide element or elements must be configured with a bend or twist along the length thereof, whereby the tilting and retracting mechanism becomes further complicated.
A failure situation, for example involving a blockage of the mechanical system of the slat arrangement, would become very critical, because then the slat could no longer be retracted if the air guide member is blocked or jammed in its deployed or extended position.
The above mentioned conference proceedings provide no suggestions toward overcoming the just mentioned significant problems and disadvantages in actually trying to carry out the proposed solution using a pivotable air guide member in practice. Especially, the prior art provides no suggestions toward a special pressure control system to be used in connection with an inflatable expandable arrangement for reducing the aero-acoustic noise generated by the slats of an aircraft wing. Particularly, the prior art does not provide any suggestions toward a system for controlling the pressure and volume of compressed air for the controlled inflation of an expandable displacement element secured on the concave rear surface of a slat in order to improve the aerodynamic contour and prevent or reduce the formation of a vortex along a slat, and thereby reduce the generation of aero-acoustic noise.
In view of the above, it is an object of the invention to provide a pressure control system for an inflatable, elastically expandable displacement element that is secured on the concave rear surface of a wing slat in order to controlledly and selectively inflate the displacement element with a controlled or regulated inflation pressure, to achieve a respective required inflation condition and shape of the displacement element. The pressure control system shall operate independently of the pressure of the bleed air system of the aircraft, and shall require a minimum of operating power or particularly a minimum of bleed air. Moreover, the system shall be simple to install, and shall even be retrofittable into existing aircraft, while also requiring only a simple maintenance. The invention further aims to overcome or avoid the disadvantages of the prior art, and to achieve additional advantages, as apparent from the present specification.
The above objects have been achieved according to the invention in a pressure control system for regulating or controlling the supply of compressed air to an elastically expandable hollow displacement element of an arrangement for reducing the aero-acoustically generated noise of a wing slat of an aircraft. Particularly according to the invention, the pressure control system includes a shut-off valve with a respective valve controller, a pressure regulating (or control) valve with a respective valve controller, and a wing slat contour controller or regulating device that is connected by respective data signal lines to a the respective valve-controllers of the shut-off valve and the pressure regulating valve. The shut-off valve and the pressure control valve are interposed in series in a bleed air line that is connected from a bleed air system of the aircraft to an inflatable hollow space within the elastically expandable displacement element which is secured on the concave rear surface of the wing slat. The shut-off valve controls the supply of compressed engine bleed air through the bleed air line to the displacement element, based on a defined air quantity or volume that is to be supplied into the displacement element for inflating the same. The pressure regulating (or control) valve monitors and regulates the air pressure of the compressed engine bleed air being supplied into the displacement element.
With the inventive pressure control system, the displacement element can be safely and precisely inflated to the required inflated shape to achieve a respectively required configuration or overall profile contour of the slat including the displacement element, for a particular flight condition. The displacement element can be properly inflated regardless of the possibly varying system pressure of the aircraft bleed air system. Also, the displacement element is protected against over-pressure conditions which could otherwise cause a bursting rupture of the displacement element. The inventive pressure control system also provides for the proper controlled deflation of the displacement element, when the displacement element is to be contracted into a contracted configuration for retracting the slat against or onto the leading edge nose of the main wing. Also, the inventive system is able to monitor or test the airtight condition of the inflatable displacement element, by pressurizing the element, closing the shut-off valve, and then monitoring the pressure of the air confined in the element.